Noctua Low-Noise Adaptor

[Shrek]

The brown Noctua 4-pin fans come with a Low-Noise Adaptor

I don't really want to break mine apart, but does anyone know how the magic is done?

I assume they reduce the duty cycle but was wondering about the details; then again there are also low noise adaptors for their 3-pin fans, so it may not be a PWM thing. Maybe just a resistor in the power line?

 

[AsRock]

Never looked but maybe a resistor ?.

 

[cvaldes]

The brown Noctua 4-pin fans come with a Low-Noise Adaptor

I don't really want to break mine apart, but does anyone know how the magic is done?

I assume they reduce the duty cycle but was wondering about the details; then again there are also low noise adaptors for their 3-pin fans, so it may not be a PWM thing. Maybe just a resistor in the power line?

Yes, I think it's a resistor on pin 2. It knocks off about 17% of the voltage based on fan RPM measurements I've taken. I did not bother to put my multimeter on it.

The 3-pin Noctua LNA behaves similarly. So if the motherboard sends 12V to the fan header about 10V makes it to the fan motor.

I assume the other wires are connected normally (GND on pin 1, SENSE on pin 3, and PWM control on the 4-pin model). The 4-pin LNA does not mess with PWM.

Sometimes these are handy even if I don't need the low-noise reduction but I do want a 10cm fan cable extension instead of a 30cm extension. I don't run any of my PC fans at 100% speed so I don't really care if I limit a fan to 83% of its maximum RPM.

 

[Courier 6]

3 ohm or close to that resistor, you could make it yourself if you wanted, very simple

 

[Shrek]

Good to know; I'm not using them at the moment but might in the future.

 

[Mussels]

They're a nifty little tool, i've used them a lot

they're definitely a resistor, i remember testing and seeing in the 10v-11v range

 

[freeagent]

Good to know; I'm not using them at the moment but might in the future.

I have a 92x35 4000rpm ripper that I use occasionally. When I do use it, it is with the 5v lna that came with my D14.. works good, but it gets hot..

 

[sam_86314]

Do note that since it's a resistor, it gets pretty hot during use.

I have one on the CPU fan on my server. It does the job, and aside from the minor concern with heat, I haven't had any issues.

 

[Shrek]

I'd not use it on a CPU fan as they are PWM and so rarely run at full speed.

 

[cvaldes]

One usage case that I didn't mention before is when you might be controlling two different fan models from the same header.

I have a mini-ITX mobo in an NZXT H210 case; the CPU and AIO fan headers are already being used leaving the third and last fan header for the case fans. I have a Noctua NF-P14r redux-1500 on the case top and a Noctua NF-S12B redux-1200 in the back on a Y-splitter adapter cable. I set the PWM fan curve based on the 140mm top fan. Since the 120mm is the secondary fan, there's no PWM control, its speed is being solely controlled by voltage.

By putting the 4-pin Noctua LNA on the 140mm top fan, I reduce its 1500 rpm top speed to about 1250 rpm. That's real close to the 1200 rpm max speed of the 120mm fan. Thus using the Noctua LNA, I can have both the 120mm back fan and the 140mm top fan run around the same rpm even though I'm only sending PWM control signals to the latter.

Yes, I could buy some aftermarket fan controller hub but this is one usage case where the dumb LNA works.

 

[Mussels]

I'd not use it on a CPU fan as they are PWM and so rarely run at full speed.

#NotAllCPUFans


Mine all ended up in older 3 pin systems, now that i think of it - definitely be careful about high wattage fans or multiple fans as they can heat up or even melt (which is why noctua went with a fairly low resistance, it's on the safer side)

 

[sam_86314]

I'd not use it on a CPU fan as they are PWM and so rarely run at full speed.

It has a server board with absolutely terrible fan control.

 

[Shrek]

I measured my Noctua low noise adaptor and got about 50 Ω

• The 92mm fan (NF-A9 PWM) is 12 V, 0.1 A and so 120 Ω; so, with 50 Ω in series, 12 V is reduced to about 8.5 V when running flat out

which seems about right, and the resistor would then be dissipating about 1/4 W and the fan power reduced from 1.2 W to 0.6 W

• The 80mm fan (NF-A8 PWM) is 12 V, 0.08 A and so 150 Ω; so, with 50 Ω in series, 12 V is reduced to about 9.0 V when running flat out

 

[Deleted member 202104]

For Science, Sir @Shrek

Appears to be a 51 Ohm, 5% (if i remember/read this correctly)

 

[Shrek]

Thanks Opus, greatly appreciated